Electron microscopes



g- 2, 1955 o. WOLFF 2,714,678

ELECTRON MICROSCOPES Filed Aug. 29, 1951 3 Sheets-Sheet l J 57 V i .5; r 65 g ..75.19 '2'? 4 J HM v Aug. 2, 1955 o. WOLFF 2,714,678

ELECTRON MICROSCOPEIS Filed Aug. 29, 1951 5 Sheets-Sheet 2 -,"I i 6 I x f Z I!!!) 20 I, /JZ 70 34 l 42 Z7 1- I! 2 g3 a I i 1 V i j g E M if I .JFzvem 077 Aug. 2, 1955 o. WOLFF 2,714,678 ELECTRON MICROSCOPES Filed Aug. 29, 1951 5 Sheets-Sheet '3 a N WITH";

United States Patent Ofitice 2,714,678 Patented Aug. 2, 1955 2,714,678 ELECTRON MrcnoscoPEs Otto Wolff, Berlin-Frohnau, Germany, assignor to Siemens 8; Halske Aktiengesellschaft, Munich, Germany, a corporation of Germany Application August 29, 1951, Serial No. 244,195 15 Claims. (Cl. 31384) This invention relates to electron microscopes, and is particularly concerned with a multiple-lens image-forming system for such microscopes.

The use in electron microscopes of multiple-lens systems comprising three and even four electron lenses for the formation of the image of a specimen is broadly known. In a prior embodiment operating with electromagnetic lenses the regulation of the refractive power of the objective has been used for the focusing of the image, while an intermediate lens served for the adjustment of the final image magnification. The operation of the projective lens with fixed refractive power gave in such cases the possibility to fully illuminate a predetermined diameter of the final image in any operating position. The refractive power is in such case adjusted by regulating the current in the exciting circuit of the lenses.

The invention has to do with a four-lens image-forming system which is preferably operated with permanent magnet excitation. A pole shoe member is provided forming the lens gaps for the two intermediate lens. The pole shoe member is, for the regulation of the magnification, axially adjustable. The magnetic flux is conducted to a central portion of the pole shoe member over a magnetic regulator, e. g., through the medium of a rotatable regulator. The latter serves for the focusing of the image. It is possible to obtain in this manner, by simple means, the required operating positions (focusing and regulation of magnification) and to fully illuminate a certain final image diameter in any operating position.

A particularly simple structural embodiment is, in accordance with a further object and feature of the invention, obtained by slidably disposing the opposite ends of the above mentioned axially movable pole shoe member of the two intermediate lenses in guide bores which are provided in the pole shoe members of the objective and the projective, respectively. The central portion of the axially movable pole. shoe member is journalled or guided in a bore of a stationary ringor disk-shaped member of magnetic material which may be provided a suitable drive means, e. g., with gear wheel journalled therein, which is operable from its outside and meshes with gear teeth formed on the member for elfecting the axial adjustment. The variable flux may be conducted to the outer rim of the disk member through the medium of a rotatable regulator which serves for the focusing.

The. excitation of the four lenses of such an imageforming systemmay be accomplished in several ways. A particularly simple arrangement for the excitation. of all four lenses is obtained. by the use of two cylindrical permanent magnets which are associated with the objective and: with the projective, respectively.

The foregoingobjects and other objects and features of the invention will appear from the description which will presently be rendered with reference to the accompanying drawings. In these drawings,

Fig. 1 shows an embodiment of the invention in diagrammatic longitudinal section;

Fig. 2 is a fragmentary transverse section taken through Fig. 1 approximately along the line 2-2 thereof; and

Figs. 3 and 4 illustrate in similar diagrammatic manner modifications.

Numeral 1 in Fig. 1 designates the lens gap of the objective; 2 and 3 are annular grooves in the regulating member 20 forming the lens gaps of the two intermediate lenses; and 4 is the lens gap of the projective. The lens gap 1 of the objective is formed by the two pole shoe members 5 and 6, and the lens gap 4 of the projective is formed by the two pole shoe members 7 and 8. The annular grooves 2 and 3 provide constricted portions in the material of the member 20, causing the magnetic lines of force to form at these constricted portions outside thereof so as to create at the corresponding areas magnetic fields which produce the intermediate lens effects. The two outer pole shoe members 5 and 8 may be parts of or associated with the two respective transverse casing walls 9 and 10. It is possible of course to form these pole shoe members as separate members and to insert them in suitable manner in the corresponding transverse casing Walls. The entire system is closed to the outside by the cylindrical outer casing wall 11 which is suitably assembled together with the transverse walls 9 and 10.

u The casing wall fill and also the transverse walls 9 and 10 are made of magnetic material. Numerals 12 and 13 designate permanent magnets which. serve for the excitation of the lenses. These magnets are cylindrical inform and, as is apparent from Fig. I, serve also for spacing and for holding the pole shoe members 6 and 7 relative to the corresponding transverse walls 9 and 10. The magnets are positioned. so that the casing is connected with poles of identical sign, making the entire arrangement free of an outwardly effective magnetic field.

Between the annuiar radially outwardly extending portions of the pole shoe members 6 and 7 is disposed the disklike member 16 which is held in stationary position by the tubular nonmagnetic members 14 and 15. The disklike member 16 is made of magnetic material and formswith a rotatable annular member 17 a regulator for the focusing. The two intermediate lenses 2 and 3 receive variable amounts of magnetic flux, depending on the adjustment of the regulator member 17, the flux extending over the teeth 19 which project radially outwardly from the stationary disklike member 16 for coaction with the teeth 18 which project radially inwardly from the 1:0- tatable regulator member E7.

The mechanical means for rotating the regulator member 17 relative to the disklike member 16 may be any suitable and desired gearing means. For example, the regulator member 17 may be suitably. journalled. on the inside of the casing wall 11 and may be provided with an annular gear 61 for coaetion with a pinion 62 on a shaft which extends in vacuumtight manner to the outside and carries an operating member such as a knob 63 or the like for rotating it, so as to rotate the regulator member 17 as described. The knob 63 may be provided with a pointer 64 for coaction with a suitably secured scale 65 to indicate the focusing adjustment.

The regulation of the final image magnification is obtained by axial displacement of the pole shoe member 20 which forms the two intermediate lens 2 and 3. The opposite ends of the. member 249 are for this purpose movably journalled in. the bores 21, 22 provided in the pole .shoe members 6 and 7 and in the central bore 23 in the disk 16. The displacement is effected by means of the gear wheel 24 which is journalled in the stationary disk 16 andmeshes with teeth 25 on the member 20. The gear wheel 24 is provided with a shaft 66 extending therefromto the outside in vacuumtight manner through the casing wall 11 and carrying a knob 67. The knob 67 may be provided with a pointer 68 for coaction with a suitably secured scale 69 to indicate the adjustment of the magnification. The pole shoe member 20 is indicated in Fig. 1 in full lines in one terminal position i. e., in the lower terminal position thereof. The magnification of the image will increase with increasing upward displace ment or adjustment of the pole shoe member 20 from the lowermost position in which it is shown.

The two intermediate lenses 2 and 3 are, in the example Fig. 1, formed by the integral magnetic member 20. It is possible of course to form these lenses of two separate pole shoe members in a manner as the lenses 1 and 4. Nonmagnetic spacing and holding rings may then be employed between the individual pole shoe members.

If the magnetic force of the magnets is substantially constant, the magnification on the viewing screen will in any angular position of the rotary regulator 17 depend on the axial position of the movable intermediate lens member 20.

Both drive or adjusting means (knobs 63 and 67) may be adjusted to the desired magnification of the focused image. However, the functions of the magnification adjustment (depending on the axial displacement of the member 20) and those of the focusing (depending on the angular position of the rotary regulator 17) are not generally in agreement, and the two motions may therefore be coupled or correlated by suitable means (not shown) so as to obtain an approximate focusing incident to the adjustment of the magnification and to carry out the focusing of the image by additional adjustment of the rotary regulator 17.

Parts shown in Fig. 3, which correspond to parts of Fig. 1, are identically numbered. The pole shoe member 20 carrying the annular grooves 2 and 3 forming the intermediate lenses is accordingly axially movable by the drive means indicated at 24, 25. Instead of using the rotary regulator 17, 18, 19 shown in Fig. 1, there is provided a regulator member 31 which is movable transverse to the axis of the electron stream in the directions indicated by the double arrow. In place of the tubular, nonmagnetic spacing and supporting members 14, of Fig. 1, there are in this embodiment provided two permanent magnets 32, 33. The flux from the north poles of these magnets, which is conducted to the lenses 2 and 3 over the magnetic disk 34 (corresponding to disk 16 of Fig. 1), may be continuously varied by the transverse displacement of the regulator 31. Such regulation varies the magnification of the final image.

The member 31 may be movably mounted in suitable nonmagnetic ways or brackets (not shown) carried by suitable nonmagnetic supports fixed to and extending inwardly from the inside of the casing Wall 11. The member 31 may, e. g., carry a shaft 7 (l which extends through the casing 11 to the outside, in vacuumtight manner, and is provided with a knob 71 or the like for moving the member 31 as indicated by the double arrow.

The embodiment shown in Fig. 4 employs permanent magnets disposed radially of the electron beam axis. The system containing the four-lens optics is enveloped by a casing comprising the magnetic outer tubular wall 41, a bottom transverse casing wall 42 and a suitable transverse top casing wall, which has been omitted from the drawing, thus forming an enclosure which is free of an outwardly effective magnetic field. The upper pole shoe of the objective has also been omitted from the drawing in order to make the underlying parts visible. Numeral 43 designates the lower pole shoe of the objective, and 44, 45 are the pole shoes of the projective. The axially movable member forming the two intermediate lenses (members of Figs. 1 and 3) is indicated at 47, the direction of its displacement being indicated by the double arrow 46. The member 75 is a stationary member corresponding to the member 16 of Fig. 1 (or member 34 of Fig. 3). The means for moving the member 47 to carry out the focusing may correspond to the means already explained in connection with the description of the previous figures and may comprise a gear wheel inside the member 75 (similar to the gear wheel 24, Fig. 1) meshing with teeth on the member 47 (similar to the teeth 25, Fig. 1), and a shaft 76 may extend from the gear wheel inside of the member 75 to the outside of the casing for operating the member 47 axially, as indicated by the arrows 45 For the regulation of the magnification, there is provided a rotatable regulator member 48 which is for angular displacement pivoted at shaft 49. The shaft 49 may be provided with a pinion 3t) meshing with a pinion 31 on 'a shaft 82 which extends in vacuumtight manner through the casing wall 41 to the outside and carries a knob 83. Rotation of this knob rotates the member 48 to adjust the desired degree of magnification.

For the excitation of the four lenses there are provided four permanent magnets 50 disposed in parallel relationship. The flux from these magnets is conducted to the lenses over the bracket 51.

Numerals 54, 55 indicate two regulating members which are pivotally mounted at 52 and 53, respectively. These members serve the purpose of short-circuiting the magnets during the assembly or removal thereof, and for adapting the microscope for use with variable beam voltages. The magnets may be inserted and removed together with the regulating and short-circuiting members 54, 55 through an opening in the outer casing wall 41.

Gearing means similar to those for the member 48 may be provided for adjusting the regulating members 54, 55 from the outside. Shafts or like operating members 85, 86 may extend from the pivots 52, 53 respectively. These shafts may carry pinions as indicated at 87, 88, meshing respectively with pinions 89, 90, each provided with a suitable shaft extending to the outside and carrying a suitable operating knob, as indicated at 99 and 100.

It is understood of course that the operating means described in connection with any one of the embodiments may be carried to the outside through one of the transverse lid or end walls or through the tubular side wall of the corresponding structure in a vacuumtight manner relative thereto. Scale and indicating means may be provided in the structures, Figs. 3 and 4, in the manner described in connection with Fig. 1.

Changes may be made within the scope and spirit of the accompanying claims.

I claim:

1. In an electron microscope having four serially related image-forming lenses which form, respectively, an objective, a projective and two intermediate lenses and having permanent magnet means for exciting said lenses, a relatively stationary member of magnetic material in which is formed a boring, a single pole shoe member forming said intermediate lenses, said single pole shoe member being axially movably journalled in said boring, means for axially moving said single pole shoe member to regulate the formation of the image by said lenses, and means for regulating the flux over said stationary mag netic member to aid in the formation of said image.

2. The structure defined in claim 1, wherein said fluxregulating means is a magnetic body which is movably disposed relative to said stationary magnetic member in the radial plane thereof.

3. The structure defined in claim 1, wherein said fluxregulating means is a magnetic body which extends substantially in parallel with said axially movable pole shoe member.

4. The structure defined in claim 1, wherein said fluxregulating means is a magnetic body which extends substantially in parallel with said axially movable pole shoe member, and means for moving said flux-regulating body relative to said pole shoe member in a direction transverse to the axis thereof.

5. The structure defined in claim 1, wherein said fluxregulating body is a magnetic body which extends radially of said stationary magnetic member. and means for pivotally mounting said flux-regulating lar displacement of its free end relative to magnetic member.

6. The structure defined in claim 1, together with means for variably short-circuiting said permanent magnet means.

7. The structure defined in claim 1, together with means for variably short-circuiting said permanent magnet means comprising a pair of magnetic members, and means for mounting said members for displacement relative to said permanent magnet means.

8. The structure defined in claim 1, together with means for variably short-circuiting said permanent magnet means comprising a pair of magnetic members, means for pivotally mounting said members at points adjacent identical poles of said permanent magnet means, and means for angularly moving said members to displace the free ends thereof relative to the other poles of said permanent magnet means.

9. An electron microscope comprising means forming respectively an objective and a projective lens, an axially movable pole shoe member forming two intermediate lenses, permanent magnet means for exciting said lenses, borings being formed in the means forming said objective and said projective lenses for axially movably journalling said axially movable pole shoe member, and means for axially moving said pole shoe member to regulate the magnification of the image formed by said lenses.

10. An electron microscope comprising means forming respectively an objective and a projective lens, an elongated axially movable pole shoe member forming two intermediate lenses, permanent magnet means for exciting said lenses, a relatively stationary member of magnetic material disposed approximately midway of the opposite ends of said elongated axially movable pole shoe member, borings being formed in the means forming said objective and said projective lenses for axially movably journalling said elongated axially movable pole shoe member, and means for axially moving said pole shoe member to regulate the magnification of the image formed by said lenses.

11. An electron microscope comprising means forming respectively an objective and a projective lens, an elongated axially movable pole shoe member forming two intermediate lenses, permanent magnet means for exciting said lenses, a relatively stationary member of magnetic material disposed approximately midway of the opposite ends of said elongated axially movable pole shoe member, said axially movable pole shoe member being journalled in said relatively stationary member, borings body for angusaid stationary being formed in the means forming said objective and said projective lenses for axially movably holding the opposite ends of said elongated axially movable pole shoe member, gear means in said relatively stationary memher, and means for operating said gear means for the purpose of axially moving said axially movable pole shoe member to regulate the magnification of the image formed by said lenses.

12. An electron microscope comprising means forming respectively an objective and a projective lens, an axially movable pole shoe member forming two intermediate lenses, permanent magnet means for exciting said lenses, a relatively stationary member of magnetic material disposed approximately midway of the opposite ends of said elongated axially movable pole shoe member, said axially mova le pole shoe member being movably journailcd in said relatively stationary member, means for regulating tr e flux flowing through said relatively stationary member, and means for axially moving said axially movable pole shoe member to regulate the magnification of the image formed by said lenses.

13. An electron microscope having means forming four serially related image-forming lenses, said means comprising first and second pole shoe members forming respectively an objective and a projective lens and a single axially movable pole shoe member forming two inter- References Cited in the file of this patent UNITED STATES PATENTS 2,163,157 Samuel June 20, 1939 2,369,782 Hillier Feb. 20, 1945 2,369,796 Ramberg Feb. 20, 1945 2,494,442 Le Poole Jan. 10, 1950 2,579,273 Reisner Dec. 18, 1951 

